3.2: Metric Prefixes

For hundreds of years, the languages of the educated class were Latin and Greek, in part because the literature of philosophy was in Latin or Greek. Even the medieval Bibles were written in those two languages - the first English translation was in the late 1380's. Using Latin and Greek allowed scholars from different countries to communicate more easily with one another. Today we still see many Latin phrases in legal communications ("pro bono" meaning to do something "for the good" and not charge legal fees), scientific naming of biological species, and Latin is used for the annual student speech at Harvard University graduations. Not bad for a "dead" language.

Metric Prefixes

Conversions between metric system units are straightforward because the system is based on powers of ten. For example, meters, centimeters, and millimeters are all metric units of length. There are 10 millimeters in 1 centimeter and 100 centimeters in 1 meter. Metric prefixes are used to distinguish between units of different size. These prefixes all derive from either Latin or Greek terms. For example, mega comes from the Greek word \(\mu \varepsilon \gamma \alpha \varsigma\), meaning "great". Table \(\PageIndex{1}\) lists the most common metric prefixes and their relationship to the central unit that has no prefix. Length is used as an example to demonstrate the relative size of each prefixed unit.

Table \(\PageIndex{1}\): SI Prefixes

Prefix

Unit Abbreviation

Meaning

Example

giga

\(\text{G}\)

1,000,000,000

1 gigameter \(\left( \text{Gm} \right) = 10^9 \: \text{m}\)

mega

\(\text{M}\)

1,000,000

1 megameter \(\left( \text{Mm} \right) = 10^6 \: \text{m}\)

kilo

\(\text{k}\)

1,000

1 kilometer \(\left( \text{km} \right) = 1,000 \: \text{m}\)

hecto

\(\text{h}\)

100

1 hectometer \(\left( \text{hm} \right) = 100 \: \text{m}\)

deka

\(\text{da}\)

10

1 dekameter \(\left( \text{dam} \right) = 10 \: \text{m}\)

1

1 meter \(\left( \text{m} \right)\)

deci

\(\text{d}\)

1/10

1 decimeter \(\left( \text{dm} \right) = 0.1 \: \text{m}\)

centi

\(\text{c}\)

1/100

1 centimeter \(\left( \text{cm} \right) = 0.01 \: \text{m}\)

milli

\(\text{m}\)

1/1,000

1 millimeter \(\left( \text{mm} \right) = 0.001 \: \text{m}\)

micro

\(\mu\)

1/1,000,000

1 micrometer \(\left( \mu \text{m} \right) = 10^{-6} \: \text{m}\)

nano

\(\text{n}\)

1/1,000,000,000

1 nanometer \(\left( \text{nm} \right) = 10^{-9} \: \text{m}\)

pico

\(\text{p}\)

1/1,000,000,000,000

1 picometer \(\left( \text{pm} \right) = 10^{-12} \: \text{m}\)

There are a couple of odd little practices with the use of metric abbreviations. Most abbreviations are lowercase. We use "\(\text{m}\)" for meter and not "\(\text{M}\)". However, when it comes to volume, the base unit "liter" is abbreviated as "\(\text{L}\)" and not "\(\text{l}\)". So we would write 3.5 milliliters as \(3.5 \: \text{mL}\).

As a practical matter, whenever possible you should express the units in a small and manageable number. If you are measuring the weight of a material that weighs \(6.5 \: \text{kg}\), this is easier than saying it weighs \(6500 \: \text{g}\) or \(0.65 \: \text{dag}\). All three are correct, but the \(\text{kg}\) units in this case make for a small and easily managed number. However, if a specific problem needs grams instead of kilograms, go with the grams for consistency.

Summary

Metric prefixes derive from Latin or Greek terms. The prefixes are used to make the units manageable.

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